It is known to mount a rotary switch on a transmission housing externally thereof to receive mechanical gear selection inputs from the operator of a vehicle through various linkages and output gear selections to appropriate output means such as a decoder module and the transmission electronic control unit via electronic signals. The switch typically includes a quadrant with a selected number of electrical switch segments disposed thereon with each segment providing an output to the output means. A manual valve controlling hydraulic operation of the transmission is mechanically coupled to a plate having indexing detents, called a detent plate, mounted on a shaft and pivotably movable therewith. The shaft extends through the transmission housing wall and a switch bar is fixedly attached to the shaft externally of the transmission housing so that when a vehicle operator selects a gear the switch bar within the rotary switch moves across the quadrant to a predetermined position to engage one or more of the electrical segments. In certain systems the electronic control monitors the gear position along with other inputs, for example, throttle position, output shaft speed, engine speed, engine load and so on.
In U.S. Pat. No. 5,736,701, assigned to the assignee of the present invention, a switch system is disclosed which is mounted within the transmission housing in order to avoid placing the switches in a hostile environment subject to water splash and the like as well as to avoid tolerance stack-up problems associated with linkages employed when mounting the switches externally of the transmission housing.
In the referenced patent, a movable electrically conductive contact assembly is mounted directly on a first face surface of the detent plate of the manual valve assembly. A generally flat quadrant shaped housing member, formed of electrically insulative material, is rotatably mounted on the manual shaft in a position adjacent to and overlying the detent plate. A stationary, electrically conductive contact assembly is disposed on a face of the housing member overlying the first face surface of the detent plate. The housing member is provided with a pair of prongs which receive therebetween the roller of a roller/spring assembly to thereby maintain the housing member in a selected X-Y position. The stationary contact assembly has a plurality of arc-shaped contact segments separated from one another in a radial direction by rib members which extend from the surface of the housing a selected distance beyond the contact segments to thereby prevent short circuiting between adjacent contact segments by debris or the like.
Switch systems made in accordance with the '701 patent are very effective in obviating the prior art hostile environment and stack-up problems; however, it is desirable to provide a lower cost system which is reliable, easily tuned and one in which changing the switching points is facilitated.
Position sensors used in transmissions often require sensing tolerances as tight as 0.7 mm (equivalent to 1° at a 20 mm radius). By reducing the number of separate components in a device, tolerance “stacks” may be distributed in a fashion that allows for maximum flexibility in part and tooling design. Additionally, the lower part count means the same stack can be divided among fewer parts, leading to larger tolerances for any individual component. Component cost can be reduced due to the looser tolerances allowed, and assembly device costs will be lower due to fewer operations that need not be as exact.